The present invention relates to pneumatic tires and, more particularly, to an improvement in radial tires having a tread reinforcement constituted by a steel cord strip layer.
Radial tires having a tread reinforcement layer constituted by steel cord strip layers exhibit much superior load bearing characteristic and durability in high-speed running to those exhibited by radial tires having a tread reinforcement layer constituted by textile cord strip layers.
The radial tires having a tread reinforcement layer constituted by steel cord strip layers, however, have some drawbacks.
Firstly, when the tread surface is damaged, water comes into the tire structure through the damage in the tread to reach the steel cord strip layers to make the latter rusty to decrease the reinforcement effect. Secondly, the steel cord strip layers, which are usually in the form of two superposed layers, impart a rough and unpleasant passenger comfort to tires incorporating the same. Thirdly, since the steel cord strip layers have a Young's modulus much greater than that of rubber, the separation of rubber from the steel cord strip layers takes place at both edges of the latter during high-speed running or under application of heavy load, resulting in a breakdown of the tire. The performance of the tire in high-speed running can be improved by selecting the width of the strip layers greater than the tread surface width. The increase of the width of the strip layers, however, increase the liability of separation of rubber from the strip layers at both edges of the latter, particularly when the cords are made of a material having a large Young's modulus as is the case with steel. Therefore, it is not allowed, practically, to increase the width of the steel cord strip layers beyond the width of the tire tread.